Passivation of metals contaminating a used cracking catalyst with certain antimony carbonates and their thio analogues

ABSTRACT

A used cracking catalyst is treated with antimony carbonate and its thio analogues to passivate contaminating metals whenever these metals have been deposited on the catalyst.

This invention relates to catalytic cracking of hydrocarbon. In one ofits aspects the invention relates to treating a used catalyst topassivate contaminating metals whenever these metals appear on thecatalyst. In another of its aspects the invention relates to a usedcracking catalyst which has been treated to passivate contaminatingmetals whenever these appear on the catalyst. In a further aspect theinvention relates to a process for the cracking of a hydrocarbonemploying a catalyst which can be contaminated with metals tending todeactivate the same, the used catalyst having been treated to passivatesuch metals or metal whenever these appear on the catalyst.

In one of its concepts the invention provides a method for treating acracking catalyst to passivate contaminating metals whenever theseappear on the catalyst by applying to the used catalyst certain antimonycarbonates and their thio analogues. In another of its concepts theinvention provides a used catalyst composition which has been modified.In a further concept of the invention it provides a process for thecracking of a hydrocarbon employing a used catalyst which has beenmodified.

Cracking catalysts, when used to crack oil that contain metals, e.g.,vanadium, iron, and nickel, accumulate a deposit of these metals, thisdecreases the yield of gasoline and increases yields of hydrogen andcoke.

This invention discloses a method to passivate said metals on the usedcatalysts bearing them. According to the invention the method involvesthe addition of certain antimony carbonates to the used catalyst, e.g.,to the metals-contaminated catalyst.

Metals-contaminated cracking catalysts that are passivated according tothe invention are any that are active to crack hydrocarbons in theabsence of added hydrogen. Included are catalysts or contact masseswhich are amorphous silica/alumina and compositions that containzeolites--synthetic or natural.

Such cracking catalyst materials can be any of those cracking catalystsconventionally employed in the catalytic cracking of hydrocarbonsboiling above 400° F. (204° F.) for the production of gasoline, motorfuel blending components and light distillates. These conventionalcracking catalysts generally contain silica or silica-alumina. Suchmaterials are frequently associated with zeolitic materials. Thesezeolitic materials can be naturally occurring, or they can be producedby conventional ion exchange methods such as to provide metallic ionswhich improve the activity of the catalyst. Zeolite-modifiedsilica-alumina catalysts are particularly applicable in this invention.Examples of cracking catalysts into or onto which antimony can beincorporated include hydrocarbon cracking catalysts obtained by admixingan inorganic oxide gel with an aluminosilicate and aluminosilicatecompositions which are strongly acidic as a result of treatment with afluid medium containing at least one rare earth metal cation and ahydrogen ion, or ion capable of conversion to a hydrogen ion. Thecatalytic cracking material employed will generally be in particulateform having a particle size principally within the range of about 10 toabout 200 microns.

If desired, the cracking catalyst can contain a combustion promoter suchas platinum or chromium.

The catalytic cracking materials can vary in pore volume and surfacearea. Generally, however, the unused cracking catalyst will have a porevolume in the range of about 0.1 to about 1 ml/g. The surface area ofthis unused catalytic cracking material generally will be in the rangeof about 50 to about 500 m² /g.

The described catalysts are generally employed for treating hydrocarbonfeedstocks at elevated temperatures to produce distillates such asgasoline and higher-boiling hydrocarbon fuels, e.g., kerosine, dieselfuel, burning oils and the like.

Passivation, as herein described, is considered to be effectedsatisfactorily whenever one of the following obtains. Gasoline yield isimproved and/or hydrogen and/or coke production is reduced.

It is an object of this invention to provide a method for passivating acatalyst having contaminating metals thereon. It is another object ofthe invention to treat the catalyst suitable for cracking a hydrocarbon,e.g., a hydrocarbon oil, to passivate contaminating metals, e.g.,vanadium, iron and/or nickel to render the same more effective for itsintended use. It is a further object of the invention to produce amodified or treated used catalyst suitable for cracking on whichcontaminating metals are passivated. It is a further object of theinvention to provide an improved hydrocarbon cracking operation.

Other aspects, concepts, objects and the several advantages of theinvention are apparent from a study of this disclosure and the appendedclaims.

According to the present invention a used catalyst suitable for crackinghydrocarbon, e.g., a hydrocarbon oil, is treated by addition of anantimony carbonate thereto, so that contaminating metals, e.g.,vanadium, iron and/or nickel thereon will be passivated.

Also according to the invention there is provided the treated catalyst.

Still according to the invention there is provided a hydrocarboncracking operation employing the modified or treated catalyst of theinvention.

The quantity of antimony to use to modify or to passivate the metal,when it has been deposited on the catalyst, should add about 0.01 to 8weight percent, preferably about 0.02 to 2 weight percent, of antimonyto the catalyst. These concentrations are expressed as the element, andare based on the weight of catalyst prior to treatment.

A variety of methods can be used to apply the antimony carbonates to thecatalyst. They can be added as finely divided solid and dispersed byrolling, shaking, stirring, etc. Or, they can be dissolved in a suitablesolvent, aqueous or organic, and the resulting solution used toimpregnate the cracking catalyst--followed by drying to remove thesolvent. Or, they can be dissolved or suspended in the oil that is thefeedstock to the cracking process where, by virtue of their negligiblevapor pressure at reaction conditions, they are retained on thecatalyst.

The antimony compounds that are effective in this invention are thecarbonates--(RXCXX)₃ Sb--wherein each X is independently selected fromoxygen and sulfur, and R preferably contains not more than 18 carbonatoms and can be alkyl, alkadienyl, alkenyl, cycloalkyl, cycloalkenyl,or aryl radical, or a combination of radicals such as alkaryl, aralkyl,alkenylaryl, and the like.

Examples of suitable carbonates, including the thio analogues, areantimony tris(propylcarbonate), antimony tris(O-propyl thiocarbonate),antimony tris(O-propyl dithiocarbonate), antimony tris(S-propyldithiocarbonate), antimony tris(S-propyl trithiocarbonate), antimonytris(ethyl carbonate), antimony tris(benzylcarbonate), and antimonytris(O-octadecylthiocarbonate).

In the examples the following compounds were used: antimony trilaurate(tridodecanoate), antimony tris(thioacetate), antimony tris(O-propyldithiocarbonate), antimony tris(dithiopentanoate), and antimonytritallate.

Feedstocks amenable to treatment by the cracking catalyst of thisinvention are, generally, oils having an initial boiling point above204° C. This includes gas oils, fuel oils, topped crude, shale oil, andoils from coal and/or tar sands.

However the oils are derived or obtained, the invention is applicable topassivate the metals on the catalyst when thereon.

The cracking process may utilize a fixed catalyst bed or a fluidizedcatalyst--this latter is preferred.

Specific conditions in the cracking zone and the regeneration zone of afluid catalytic cracker depend on the feedstock used, the condition ofthe catalyst, and the products sought. In general, conditions in thecracking zone include

Temperature: 427°-649° C. (800°-1200° F.)

Contact time: 1-40 seconds

Pressure: 10 kiloPascals to 21 megaPascals (0.1 to 205 atm.)

Catalyst:oil ratio: 3/1 to 30/1, by weight

and conditions in the regenerator include

Temperature: 538°-816° C. (1000°-1500° F.)

Contact Time: 2-40 minutes

Pressure: 10 kiloPascals to 21 megaPascals (0.1 to 205 atm.)

Air rate (at 16° C., 1 atm.): 100-250 ft³ /lb coke, or 6.2-15.6 m³ /kgcoke

It is presumed that the feedstocks to the catalytic cracker, asdescribed above, will contain a significant concentration of vanadium,iron, and/or nickel whose presence will affect adversely the catalyst'sselectivity.

Since these metals become concentrated in the least volatile fractionsof the feedstocks, the invention is especially valuable for crackingheavy oils.

The quantity of added antimony required to passivate vanadium, iron,and/or nickel is related directly to their concentration in thefeedstock. The following table relates the total concentration in thefeedstock of these metals to the concentration of added antimony on thecracking catalyst to passivate effectively these adventitious metals.

    ______________________________________                                        Total V, Fe, Ni in Antimony added to                                          Feedstock, ppm     Catalyst, wt %*                                            ______________________________________                                         40-100            0.05-0.8                                                   100-200            0.1-1                                                      200-300            0.15-1.5                                                   300-800            0.2-2                                                      ______________________________________                                         *Based on weight of catalyst prior to addition of antimony passivating        agent. Quantities are expressed as the element.                          

EXAMPLE I

This is an example according to the invention.

Antimony tris(O-propyl dithiocarbonate) was prepared by a doubledecomposition reaction between antimony trichloride and potassiumO-propyl dithiocarbonate. The latter was prepared as follows. To 22.2 g(0.395 moles) of potassium hydroxide was added 100 g (1.67 moles) ofn-propanol. This mixture was allowed to reflux for one hour; after ithad cooled to room temperature 46 g (0.60 moles) of carbon disulfide wasadded. Product precipitation began immediately. When addition of thecarbon disulfide was complete the mixture was heated to reflux for 30minutes, cooled in an ice bath, and filtered. The yellow crystals werewashed with ethanol, then with cyclohexane; they weighed 35.3 g (0.202moles).

Antimony trichloride was dried by suspending 14.1 g (0.0618 moles) inabout 200 cc tetrahydrofuran (THF) and distilling off about half of thesolvent. To it was added 26.15 g (0.15 moles) of potassium propyldithiocarbonate suspended in THF, while the antimony salt was beingrefluxed in THF. Refluxing continued about 45 minutes, during which timethe mixture had turned orange. After cooling, a considerable quantity ofsolids was removed by filtration. The filtrate contained a calculated3.57 wt% antimony as antimony tris(O-propyl dithiocarbonate). A 3.50 gportion of this solution, diluted with 30 cc of benzene, was stirredinto 25 g of Catalyst 0 (see Example I). Solvent was removed by heating,with stirring, on a hot plate. This treatment added 0.50 wt% antimony tothe catalyst. The catalyst was processed through 10 aging cycles asfollows. The catalyst, in a quartz reactor, was fluidized with nitrogenwhile being heated to 482° C., then it was fluidized with hydrogen whilethe temperature was raised from 482° to 649° C. Maintaining thattemperature, fluidization continued for 5 minutes with nitrogen, thenfor 15 minutes with air. The catalyst was then cooled to about 482° C.still being fluidized with air. The catalyst at about 482° C. wasfluidized with nitrogen for one minute, then heated to 510° C. duringtwo minutes while fluidized with hydrogen, then maintained at 510° C.for one minute while fluidized with nitrogen, then heated to about 649°C. for 10 minutes while fluidized with air, and then cooled to about482° C. during 0.5 minute while fluidized with air. After 10 such cyclesit was cooled to room temperature while being fluidized with nitrogen,and was ready for testing as Catalyst I.

Catalyst 0 and the treated catalyst were tested in a fixed bed reactorusing Kansas City gas oil as feedstock to the cracking step. Thecracking reaction was carried out at about 482° C. and atmosphericpressure for 0.5 minutes; regeneration was at about 593° C. andatmospheric pressure; the reactor was purged with nitrogen before andafter each cracking step.

Properties of the Kansas City gas oil used in the cracking steps aresummarized in Table II.

                  TABLE II                                                        ______________________________________                                        API gravity at 15.6° C.                                                                         30.2°                                         BMCI                     30.1                                                 Carbon residue, Ramsbottom                                                                             0.23 wt %                                            Analysis for some elements                                                    Carbon                   88.3 wt %                                            Hydrogen                 11.8 wt %                                            Sulfur                   0.20 wt %                                            Oxygen                   0.075 wt %                                           Nitrogen                 0.08 wt %                                            Vanadium                 9 ppm                                                Nickel                   0.25 ppm                                             Molecular wt. (number average)                                                                         328                                                  Distillation (by ASTM D 1160-61)                                               2%                      288° C.                                       10                       320                                                  20                       340                                                  30                       357                                                  50                       399                                                  70                       458                                                  90                       542                                                  Kinematic viscosity (by ASTM D 445-65)                                        at 54.4° C.       62.5 centistokes                                     at 98.9° C.       39.3 centistokes                                     ______________________________________                                    

Results of testing the catalysts as described are summarized in TableIII.

                  TABLE III                                                       ______________________________________                                                        Yield                                                                         Conversion                                                                              Coke, SCF     Gasoline                              Cat- Catalyst:oil                                                                             vol %     wt %  H.sub.2 /bbl feed                                                                     vol %                                 alyst                                                                              weight ratio                                                                             of Feed   of feed                                                                             converted                                                                             of Feed                               ______________________________________                                        0    7.13        72.4     9.4   707     44.3                                  I    7.23       76.7      7.9   373     52.6                                  ______________________________________                                    

In the example above, the metals-contaminated catalyst that had beentreated with the antimony-containing compound showed a higher gasolineyield and lower coke and hydrogen production than did the untreatedcatalyst. Conversion of feedstock increased 5.9%, gasoline yieldincreased 19%, coke yield decreased 16%, and hydrogen yield decreased47%.

U.S. Pat. No. 3,711,422, Marvin M. Johnson and Donald C. Tabler, Jan.16, 1973, discloses and claims restoring the activity of a crackingcatalyst with a compound of antimony, e.g., antimony triphenyl. U.S.Pat. Nos. 4,025,458, May 24, 1977 and 4,031,002, June 21, 1977, DwightL. McKay, disclose and claim passivating metals on unused crackingcatalysts with antimony compounds, e.g., a phosphorodithioate, asdescribed in the patents.

Reasonable variation and modification are possible within the scope ofthe foregoing disclosure and the appended claims to the invention theessence of which is that contaminating metals, e.g., vanadium, ironand/or nickel, on a used cracking catalyst are passivated by treatingthe used catalyst with an antimony carbonate, as described herein.

We claim:
 1. A cracking catalyst composition comprising a used crackingcatalyst having thereon a modifying amount of a treating agent whichcomprises an antimony carbonate.
 2. A catalyst according to claim 1wherein the antimony compound is one having the formula (RXCXX)₃ Sb,wherein each X is independently selected from oxygen and sulfur, and Rcontains not more than 18 carbon atoms.
 3. A composition according toclaim 1 wherein the antimony compound is antimony tris(O-n-propyldithiocarbonate).
 4. A hydrocarbon cracking catalyst compositioncomprising incorporated with a used cracking catalyst at least onecompound selected from the following:antimony tris(propylcarbonate),antimony tris(O-propylthiocarbonate), antimonytris(O-propyldithiocarbonate), antimony tris(S-propyl dithiocarbonate),antimony tris(S-propyl trithiocarbonate), antimony tris(ethylcarbonate), antimony tris(benzylcarbonate), antimonytris(O-octadecylthiocarbonate),and the thio analogues thereof.